Crosslinked polyacrylamide is chiefly used as profile control agents and water shutoff agents in oil recovery technology based on its excellent water absorbability to profile control certain high permeable layers and reform the permeability of the latter.
Chinese patent application No. 200410011395.1 discloses a kind of crosslinked particles poly(acrylic-acrylamide) as profile control agents employing acrylic acid and acrylamide as monomers, and bentonite or kaolin as reinforcing agents.
Moradi-Araghi, A., et al. (Water Soluble Polymers for Petroleum Recovery. Plenum, New York, 299-312.) synthesize poly(vinylpyrrolidone-acrylamide-2-acrylamido-2-methyl-propanesulfonic acid) crosslinked gel as water shutoff agent in harsh environment at a high temperature.
However, crosslinked polyacrylamide cannot be used as oil displacement agent despite its outstanding resistance to heat and salt. That's because the gel is crosslinked completely and the deformability is weak after its expansion in aqueous solution, leading to poor migration in pore throat. Besides, due to its low viscosity and obvious particles sedimentation, it has difficulty in improving mobility ratio of water and oil, that is to say, crosslinked polyacrylamide cannot increase swept volume effectively.
The use of partly hydrolyzed polyacrylamide (HPAM) as oil displacement agent is principally based on its function of increasing the viscosity of aqueous solution to enlarge swept volume and improve mobility ratio.
The larger molecular weight HPAM has, the higher the viscosity of aqueous solution is, and therefore the researchers tend to focus on increasing molecular weight of HPAM.
Chinese patent application No. 00111320.8 discloses the synthesis of anionic polyacrylamide with the molecular weight of 28,000,000˜36,000,000, indicating that ultra high molecular weight polyacrylamide is one of current developing trend of oil displacement agent. Another significant development is introducing hydrophobic association structure into linear PAM to increase viscosity of oil displacement agent and to improve its temperature and salt tolerance property.
Chinese patent application No. 02133972.4 discloses a kind of hydrophobic association polyacrylamide synthesized by copolymerization of hydrophobic monomer and acrylamide.
However, linear PAM and its modified polymers are still confronted with severe challenges in practical and those original intentions of molecular design hardly could be achieved. This is because, on the one hand, the high-temperature and high-salinity of underground environment will greatly destroy the single chain of linear polyacrylamide and it's self-assembly structures in aqueous solution. On the other hand, the poor plugging capacity of linear PAM solution to high permeability layer makes it difficult to reform permeability of the heterogeneous formation.